Add equs5or.
Add equs5or.

This is a version of equs5 which uses disjunction rather than negation
and implication.

Move exlimiv, ax11v, albidv, and exbidv earlier in the file because
they are needed for the equs5or proof. Move ax11ev too so it can stay
together with ax11v.

metamath/set.mm,metamath/set.mm,metamath/set.mm